1. Field of the Invention
The present invention relates to a core material for a noise filter, and in particular to a core material suitable to high frequency more than 200 MHz.
2. Description of the Related Art
A noise filter using a magnetic material for a core has utilized a noise controlling effect due to magnetic loss of the magnetic material of the core. For the noise filter using such magnetic material, since impedance(Z) and resistance (R) are required to be large, the core material for the noise filter should have large relative magnetic permeability and magnetic loss.
Conventionally, the noise filter using the magnetic material as the core has used a ferrite as the core material.
The noise filter using the ferrite as the core sufficiently functions as the noise filter for low frequency. However, if it is used in a domain of high frequency, a number of coils must be increased. Further, when the coil number is increased, many coils are close together and floating capacitance occurred inconveniently. Further, in an area of high frequency as 100 MHz or more, such filters cannot be used.
Unexamined Japanese Patent Publication (kokai) No. Hei 10-12442 discloses a core material for a noise filter available in wide zones as high frequency of 100 MHz or more. In the core material, two or more magnetic layers different in thickness are laminated via an insulating layer on a surface of a thin sheet of magnetic material such as permalloy.
However, this core material had defects that since the core material is produced by forming thin layers of an insulating layer and a magnetic layer through a spattering process on a thin sheet of magnetic material made of such as permalloy. Accordingly, each of processes take much time, number of the processes are many, and costs for materials are expensive.